Subsistence

Working away for several days at a time, employer pays fixed allowance. Can I claim excess costs against tax? I tend to buy food from a supermarket and self cater as the allowance provided is insufficient to cover the cost of hotels or restaurant?

Hi
No. The cost of food and drink consumed, and accommodation used,  is not in general an expense incurred wholly and exclusively for the purposes of the trade/employment, since everyone must eat in order to live.